Valve devices regulate the flow of a fluid (gases, fluidized solids, slurries, or liquids) by opening, closing, or partially obstructing various passageways. The valve includes two or more ports which allow the flow of the fluid into and out of the valve. The valve includes a valve body that houses a valve member which interfaces with a valve seat formed along the interior surface of the valve body to form a leak-tight seal when the valve member is fully closed. A valve stem is joined to or contacts the valve member and is used to transmit motion to control the position of the internal valve member with respect to the valve seat. External to the valve body, the stem is attached to a handle or other controlling device, such as a valve actuator to thereby adjust the stem and positioning of the valve member relative to the valve seat.
Valve actuators are attached to the stem to control the position of the valve member. The actuators can be electro-mechanical actuators such as an electric motor or solenoid, pneumatic actuators which are controlled by air pressure, or hydraulic actuators which are controlled by the pressure of a liquid such as oil or water. Pneumatic actuators and hydraulic actuators require pressurized air or liquid lines to supply the actuator. More specifically, the primary function of a valve actuator is to transmit the necessary mechanical force to the valve stem to move the valve member in order to produce a predetermined effect on the fluid that passes through one or more ports of the valve body. Valve actuators can be provided with power and command signals suitable for operation under various environmental conditions (e.g., temperature and pressure) and applications.